This application claims the priority of German Patent Application, Serial No. 102 03 375.7, filed Jan. 29, 2002, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.
The present invention relates to a method of securing a machine element and/or a load connected to the machine element in a fixed position.
Machine elements involved here do not have a self-locking feature and are operatively connected to an electromotive drive by which the position of the machine element is controlled directly or indirectly. A mechanical holding brake is provided to halt the machine element and/or the load.
Safety measures play an increasingly important role in conjunction with the operation of power machines. Therefore, the European Community established respective standards in 1995, as did the United States and Japan which set equivalent requirements as a consequence of e.g. domestic product liability acts. Safety issues are thus a primary focus of the industrial world market fueling a need for devices and functions that take into account safety requirements. In the field of numeric controls, the safety concept xe2x80x9cSINUMERIK SAFETY INTEGRATED(copyright)xe2x80x9d is predominantly utilized at the present time and is easily applicable also in other fields, e.g. product machines.
Another safety aspect increasingly relevant in industrial plants relates to the field of drives whose axles, shafts or other mechanics are not self-locking when the drive is switched off. In these situations there is a risk of a crash as a result of gravitational forces. Such hazardous movement can develop, for example, when vertical linear axles, in particular suspended axles, or round axles or spindles with asymmetric weight distribution, are involved. Thus, safety concerns demand proper measures to secure such axles or mechanisms in position.
One approach to address these safety concerns involves the use of a continuously active system that mechanically balances the weight. This approach is, however, complicated. Other exceptional cases involve a halting through use of socket pins, underpinning or supports. However, this proposal are targeted only for particular situations, such as reconstructions and start-up. When repeated operative activations are involved, the use of a holding brake or service brake still remains the only option.
Heretofore, a secure hold is realized by halting the electromotive drive which is determinative for the position of the machine element and/or associated load, actuating a mechanical brake to effect a relatively secure hold through frictional engagement, and subsequently switching off the drive. Despite the possibility to perform a constant check of such a brake for proper operation, this approach does not constitute a fool-proof system. While electronic concepts are indeed available to test a secure activation of the brake and it is also possible to test the friction moment in the holding mode, there is still a risk that sudden mishaps, e.g., a completely unexpected oil presence, may cause an abrupt decrease of the braking force. Operators of power machines are aware of this danger for a long time and it has therefore been proposed to use not one but several brakes to meet heightened safety demands during the holding mode. This proposal is, however, very complicated.
It would therefore be desirable and advantageous to provide an improved method for securing a machine element and/or load in a fixed position, to obviate prior art shortcomings and to attain a high degree of safety for holding the machine element and/or load in place.
According to one aspect of the present invention, a method of securing in a fixed position a machine element whose position is directly or indirectly controlled by an electromotive drive in the absence of a self-locking mechanism, includes the steps of halting the drive and activating a brake to maintain the machine element in a holding position, and maintaining the drive in an active mode to maintain the holding position, whereby the drive is a safe drive constructed to securely prevent a re-starting although an inadvertent shutdown is not preventable.
Heretofore, conventional wisdom required a shutdown of the drive in the holding position as the only option because of the consideration that an inadvertent re-starting of the drive poses a threat to the holding system. The present invention now recognizes that such an inadvertent starting can be safely prevented by suitable measures to establish a xe2x80x9csecure drivexe2x80x9d so that this conventionally perceived threat is no longer an issue. Thus, the drive can be surprisingly used as redundant, electrical holding system which is completely independent from the mechanical brake.
According to another feature of the present invention, control parameters can be so adapted that positional changes of the holding position below a predetermined threshold are tolerated by a controller. In this way, a very good adaptation to the stationary operation is ensured.
According to another feature of the present invention, the control parameter can be varied in a stabilizing manner in the holding position. Thus, the risk of excitation of undesired vibrations is minimized.